Gum Bichromate Process 

What is a gum bichromate photographic print?
Gum bichromate is a deceptively simple process which involves just a single light sensitive chemical, is developed in water, and can be printed on a variety of papers.  

The basic outline of the procedure of gum printing.
The gum print process works on the principle that an organic colloid (in this case gum Arabic) when combined with a dichromate becomes light sensitive. Exposure of this dichromated colloid to a UV light source causes the organic colloid (gum arabic) to harden in proportion to the light striking it. Adding watercolor pigment to the gum provides the color. Development is achieved by floating the exposed print in water for 30 minutes or more. The unhardened gum is washed away, leaving the hardened, exposed gum to form the image on the paper.

The gum print, unlike most traditional photographic prints, can be physically manipulated to a considerable extent. During development, when the print is wet and fragile, details can be rubbed out with the use of a brush. Images can be re-sensitised and re-exposed several times, either to deepen tone or to achieve definite color shifts.  Most images are three to thirty layers of pigment. Paper choice, intensity of pigment and other factors all affect the number of coats possible.  I use Rives BFK watercolor paper, excusively.

Most photographic processes are essentially the product of chemical interaction, but gum printing is a balance between chemical and physical interaction. 

Reflections on photographic printmaking
My interest lies in both the image and the manner in which it was made. Investigating 19th century photography brings an appreciation of the rich variety of printmaking methods that have been used during photography's history. Continuing to practice these early processes ensures that the diversity of photo-printmaking is not lost in an era where photographic technology is changing rapidly towards digital.  I enjoy the painterly quality of this photographic medium, and the depth and history that is created by the layers of pigment.